The DUP’s decision to demand a further official police probe comes after a delegation including Mr Poots met with PSNI Chief Constable Matt Baggott last night to discuss the case.

A senior source said: “We are keen to see this properly investigated by an external police force. Otherwise too many questions are left unanswered.”

The party’s decision came as it emerged the decision against prosecuting the Sinn Fein president is to be reviewed by Northern Ireland Attorney General John Larkin.

Mr Larkin has been asked to examine what — and when — Mr Adams told police about his brother Liam, who is due to be sentenced on November 5 in Belfast for sexually abusing his daughter Aine in the 1970s.

The decision was announced by the Director of Public Prosecutions, Barra McGrory, who was the lawyer for Mr Adams during the child abuse probe involving Liam. The Public Prosecution Service said on taking up the job Mr McGrory had flagged up his prior involvement in the case and had no involvement in any decisions around it.

A statement from the Public Prosecution Service said: “While the director has confidence in the evidential decision taken by the PPS prior to his appointment, he has asked the Attorney General to independently review the matter.

“The Attorney General will be given full access to all materials that he considers necessary in order to complete this review.”

Mr Adams has insisted that the police were aware of the allegations against his brother as far back as 1987 but he came under increased questioning over his failure to make a fuller statement in the nine years after his brother came clean.

Mr Adams said: ”It is clear that there are some politicians and elements in the media who have decided to use this issue for opportunistic and party political reasons and who seek to politicise what is at its heart a family tragedy.”

Gerry Adams first heard in 1987 that his brother Liam had abused his niece Aine.

He told his brother’s first trial, which collapsed earlier this year, that Liam had confessed in 2000 but admitted he did not pass that information to the police for another nine years. Mr Larkin is expected to take two weeks to review the evidence in the case.